1. Field of the Invention
The invention relates to an image forming apparatus of the electrophotographic type, and specifically to an image forming apparatus having cleaning means for cleaning an electrophotographic photosensitive member.
2. Description of Related Art
[Background of the Electrophotographic Apparatus]
In recent years, an organic photoconductor (hereinafter referred to as the OPC) having an organic photoconductive material has been widely utilized as the electrophotographic photosensitive member (hereinafter simply referred to as the photosensitive member) of an image forming apparatus of the electrophotographic type. The OPC has such advantages as the case with which a material coping with various exposure wavelengths is developed, and a low cost of manufacture, but is weak in mechanical strength and the surface of the photosensitive member is liable to be deteriorated during a great deal of print, and in some cases, there has arisen the problem that the surface of the photosensitive member is liable to be injured.
Particularly recently, as the needs of the market, importance has been attached to such characteristics as long life and maintenance freedom, in addition to coloring and a higher quality of image.
Specifically, importance has been attached to such characteristics as the stabilization of a latent image and visualized image characteristic, and an anti-wear property, and more importance has come to be attached to the durability against the chemical deterioration, mechanical deterioration and electrical deterioration of the photosensitive member and a system.
In an electrophotographic image forming apparatus using the usually used Carlson method, the photosensitive member is repetitively subjected to the charging, exposing, developing, transferring and cleaning steps and therefore, there is the high possibility of the wear of the photosensitive member and the adherence of foreign substances thereto being caused by electrical and mechanical extraneous forces.
From such a background, the electrophotographic photosensitive member is required to have durability against chemical, electrical and mechanical extraneous forces such as the chemical deterioration by ozone and nitrogen oxides during charging, and the mechanical deterioration and electrical deterioration by discharge during charging and the rub of a cleaning member.
Various studies have been made in order to satisfy the various characteristics required as noted above.
For example, in order to improve the durability of the above-described OPC, there has been studied the technique of improving the anti-discharge stability of the OPC and the durability thereof against mechanical deterioration and electrical deterioration.
As an approach to it, in the above-described OPC, there has been reported a method of using hardenable resin as resin for a charge transporting layer (for example, Japanese Patent Application Laid-open No. H02-127652).
Also, there has been reported an OPC using hardenable resin containing a charge transporting material, and further provided with a lubricant and an oxidation preventing function (for example, Japanese Patent Application Laid-open No. 2001-175016, Japanese Patent Application Laid-open No. 2002-040686, Japanese Patent Application Laid-open No. 2001-166520, Japanese Patent Application Laid-open No. 2002-236382 and Japanese Patent Application Laid-open No. 2001-265044).
However, an increase in the mechanical strength of the OPC and a reduction in the abrasion speed thereof have sometimes caused a case where it becomes difficult to remove adhering materials attributable to a toner, paper dust, etc. adhering to the surface of the photosensitive member which have heretofore been effectively removed by abrasion, and as a result, the lowering of the quality of image such as image deletion under a high humidity environment is caused by the accumulated adhering materials.
As improving means for such case, there have been reported a method of prescribing, in a system wherein there are disposed a photosensitive member having an outermost surface formed of resin having cross-linking structure, and cleaning means comprising a cleaning blade, and further having a brush roller for assisting in cleaning, the shape characteristic of the brush roller and such installation conditions to the photosensitive member as the push pressure with which the brush roller is pushed against the photosensitive member, and driving torque (for example, Japanese Patent Application Laid-open No. 2001-051576), and a method of prescribing the range of an expression comprising the shape characteristics of the brush roller such as the thickness of fiber and brush density, the Young's modulus of the brush, the installation conditions to the photosensitive member and the driving condition (for example, Japanese Patent Application Laid-open No. 2002-182536).
Japanese Patent Application Laid-open No. 2001-051576, however, discloses nothing regarding the result of image such as image deletion. Also, in Japanese Patent Application Laid-open No. 2002-182536, it is described that an abrasion speed less than 0.45 μm/200 kc (1 kc=1000 copies) is insufficient for the prevention of the deterioration of the photosensitive member.
Also, in the above-described methods, even under a condition in which the so-called ordinary image deletion can be suppressed and as a matter of course, cleanability is good, there has been a case where a streak-like image defect is caused by wear resistance (plate wear). Such a streak-like defect is halftone on the high light side and is easy to see. This is a problem particularly in a color image forming apparatus which outputs such an image, and is a greater problem in an apparatus aiming at a high quality of image.
About the streak-like image defect caused by the print resistance, we have compared and evaluated various photosensitive members differing in abrasion resistance from one another with a result that it has been found that such a defect is liable to occur to a photosensitive member which is small in abrasion speed, that is, high in abrasion resistance.